Curable compositions

ABSTRACT

Curable compositions, such as benzoxazine-based ones, are useful in applications within the aerospace industry, such as for example as a heat curable composition for use as a matrix resin or an adhesive, and form the basis of the present invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.10/607,111, filed Jun. 27, 2003 now U.S. Pat. No. 7,157,509.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Curable compositions, such as benzoxazine-based ones, are useful inapplications within the aerospace industry, such as for example as aheat curable composition for use as a matrix resin or an adhesive, andform the basis of the present invention.

2. Brief Description of Related Technology

Epoxy resins with various hardeners have been used extensively in theaerospace and electronics industries both as adhesives and as matrixresins for use in prepreg assembly with a variety of substrates.

Benzoxazines themselves have been reported in the literature asgenerally having a high glass transition temperature, good electricalproperties (e.g., dielectric constant), and low flammability.

Blends of epoxy resins and benzoxazines are known. See e.g. U.S. Pat.No. 4,607,091 (Schreiber), U.S. Pat. No. 5,021,484 (Schreiber), U.S.Pat. No. 5,200,452 (Schreiber), and U.S. Pat. No. 5,445,911 (Schreiber).These blends appear to be potentially useful in the electronicsindustry, as the epoxy resins can reduce the melt viscosity ofbenzoxazines allowing for the use of higher filler loading whilemaintaining a processable viscosity. However, epoxy resins oftentimesundesirably increase the temperature at which benzoxazines polymerize.

Ternary blends of epoxy resins, benzoxazine and phenolic resins are alsoknown. See U.S. Pat. No. 6,207,786 (Ishida), and S. Rimdusit and H.Ishida, “Development of new class of electronic packaging materialsbased on ternary system of benzoxazine, epoxy, and phenolic resin,”Polymer, 41, 7941-49 (2000).

Other resins, such as reactive monomers, polymers and oxazolines,polyimide/siloxane co-polymers and cyanate esters, are too known. Seee.g. U.S. Pat. No. 4,806,267 (Culbertson), in connection with oxazolinesand J. McGrath et al., “Synthesis and Characterization of SegmentedPolyimide-Polyorganosiloxane Copolymers”, Advances in Polym. Sci., Vol.140, Springer-Verlag, Berlin 61-105 (1999) in connection withpolybenzoxazine polyimide-polyorganosiloxane co-polymers.

Moreover, in J. Jang et al., “Performance Improvement of Rubber ModifiedPolybenzoxazine”, J. Appl. Polym. Sci., 67, 1-10 (1998), the authorsreport the use of polybenzoxazine modified with amine-terminated,butadiene acrylonitrile rubber and with carboxyl-terminated, butadieneacrylonitrile rubber to improve mechanical properties. Thepolybenzoxazine chosen was synthesized from bisphenol A, formaldehydeand the aromatic amine, aniline.

Notwithstanding the state of the technology, there has been nodisclosure, teaching or suggestion to prepare a heat curable compositionbased on the combination of a benzoxazine prepared from bisphenol A,formaldehyde and alkyl amines, and amine-terminated, butadieneacrylonitrile rubber, let alone one with improved performanceproperties.

SUMMARY OF THE INVENTION

The inventive compositions include a heat curable composition comprisingthe combination of a benzoxazine component and a toughener component.

In one aspect, the invention provides a benzoxazine component comprising

where o is 1-4, X is a direct bond (when o is 2), alkyl (when o is 1),alkylene (when o is 2-4) , carbonyl (when o is 2), thiol (when o is 1),thioether (when o is 2) , sulfoxide (when o is 2), and sulfone (when ois 2), and R₁ is alkyl, such as methyl, ethyl, propyls and butyls; and atoughener component comprising acrylonitrile-butadiene co-polymer havingsecondary amine terminal groups (“ATBN”).

In a more specific embodiment of that aspect of the invention, thebenzoxazine component is embraced by

where X is selected from the group consisting of a direct bond, CH₂,C(CH₃)₂, C═O, S, S═O and O═S═O, and R₁ and R₂ are the same or differentand are selected from methyl, ethyl, propyls and butyls.

In yet a more specific embodiment of that aspect of the invention, thebenzoxazine component is embraced by

where R₁ and R₂ are the same or different and are selected from methyl,ethyl, propyls and butyls, though in a particularly desirable embodimentR₁ and R₂ are each methyl.

Cured reaction products of the inventive compositions are capable ofdemonstrating at least one of a wet Tg of at least 350° F., such as inthe range of 350 to 455° F., a toughness measured by G_(Ic) of at least1.9 in-lb./in², such as in the range of 1.9 to 4.0 in-lb./in², a percentdecrease in ΔH of at least 15% compared with a benzoxazine prepared frombisphenol F and aniline, and a percent decrease in wet Tg compared withdry Tg with increased toughener concentration of less than 6%.

Cured reaction products of the inventive compositions are also capableof demonstrating a Tg and toughness measured by GI_(c) increase as theamount of toughener in the composition increases.

Moreover, cured reaction products of the inventive compositions shouldalso have a cured density of less than 1.2 g/cc.

The invention is further directed to prepregs of the inventivecompositions and cured reaction products thereof, prepregs of theinventive compositions and cured reaction products thereof, towpregs ofthe inventive compositions and cured reaction products thereof, andprocesses for producing the prepregs and towpregs, adhesive compositionsof the inventive compositions and films thereof, methods of preparingand using the inventive compositions, articles of manufacture assembledwith the inventive compositions and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a plot of glass transition temperature (left y axis) vs.toughness vs. G_(IC) (right y axis) for benzoxazine with increasing ATBNconcentration.

FIG. 2 is a representation of FIG. 3 from J. Jay et al., depicting aplot of G_(IC) vs. ATBN and acrylonitrile-butadiene co-polymer havingcarboxyl terminal groups (“CTBN”) concentration.

FIG. 3 is a representation of FIG. 6 from J. Jay, et al., depicting aplot of Tg vs. ATBN and CTBN concentration.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the present invention provides generally a heat curablecomposition comprising the combination of a benzoxazine component and atoughener component.

In one aspect, the invention provides a benzoxazine component comprising

where o is 1-4, X is a direct bond (when o is 2), alkyl (when o is 1),alkylene (when o is 2-4), carbonyl (when o is 2), thiol (when o is 1),thioether (when o is 2), sulfoxide (when o is 2), and sulfone (when o is2), and R₁ is alkyl, such as methyl, ethyl, propyls and butyls; and atoughener component comprising ATBN.

In a more specific embodiment of that aspect of the invention, thebenzoxazine component is embraced by

where X is selected from the group consisting of a direct bond, CH₂,C(CH₃)₂, C═O, S═O and O═S═O, S, and R₁ and R₂ are the same or differentand are selected from methyl, ethyl, propyls and butyls.

In yet a more specific embodiment of that aspect of the invention, thebenzoxazine component is embraced by

where R₁ and R₂ are the same or different and are selected from methyl,ethyl, propyls and butyls, though in a particularly desirable embodimentR₁ and R₂ are each methyl.

Cured reaction products of the inventive compositions are capable ofdemonstrating at least one of a wet Tg of at least 350° F., such as inthe range of 350 to 450° F., a toughness measured by G_(Ic) of at least1.9 in-lb./in², such as in the range of 1.9 to 4.0 in-lb./in², a percentdecrease in ΔH of at least 15% compared with a benzoxazine prepared frombisphenol F and aniline, and a percent decrease in wet Tg compared withdry Tg with increased toughener concentration of less than 6%.

Cured reaction products of the inventive compositions are also capableof demonstrating improved Tg and toughness measured by GI_(c) increaseas the amount of toughener in the composition increases.

Moreover, cured reaction products of the inventive compositions shouldalso have a cured density of less than 1.2 g/cc.

The benzoxazine component should be present in an amount in the range ofabout 10 to about 99 percent by weight, such as about 25 to about 75percent by weight, desirably about 35 to about 65 percent by weight,based on the total weight of the composition.

The toughener component, ATBN, should be present in an amount in therange of about 1 to about 90 percent by weight, such as about 10 toabout 70 percent by weight, desirably about 15 to about 30 percent byweight, based on the total weight of the composition.

The benzoxazine component of the present invention may typically beprepared by reacting a phenolic compound, such as a bisphenol A,bisphenol F, bisphenol S or thiodiphenol, with an aldehyde and an alkylamine. U.S. Pat. No. 5,543,516, hereby expressly incorporated herein byreference, describes a method of forming benzoxazines, where thereaction time can vary from a few minutes to a few hours, depending onreactant concentration, reactivity and temperature. See also Burke etal., J. Org. Chem., 30(10), 3423 (1965); see generally U.S. Pat. No.4,607,091 (Schreiber), U.S. Pat. No. 5,021,484 (Schreiber), U.S. Pat.No. 5,200,452 (Schreiber) and U.S. Pat. No. 5,443,911 (Schreiber).

Benzoxazines are presently available from several sources commercially,including Vantico, Inc., Brewster, N.Y., Georgia-Pacific Resins, Inc.and Shikoku Chemicals Corporation, Chiba, Japan, the least of whichoffers among others B-a, B-m, F-a, C-a and F-a benzoxazine resins. Ofthese, the benzoxazine component of the present invention is oftentimesdesirably within the B-m benzoxazine resin family.

Benzoxazine polymerization can also be initiated by cationic initiators,such as Lewis acids, and other known cationic initiators, such as metalhalides; organometallic derivatives; metallophorphyrin compounds such asaluminum phthalocyanine chloride; methyl tosylate, methyl triflate, andtriflic acid; and oxyhalides.

The inventive compositions may also include coreactants, curativesand/or catalysts for the benzoxazines component. Examples include Lewisacids, such as phenols and derivatives thereof, strong acids, such asalkylenic acids and cationic catalysts.

The invention relates also to prepregs formed from a layer of fibersinfused with the inventive heat curable composition.

In this regard, the invention relates also to a processes for producinga prepreg. One such process includes the steps of (a) providing a layerof fibers; (b) providing the inventive heat curable composition; and (c)joining the heat curable composition and the layer of fibers to form aprepreg assembly, and exposing the resulting prepreg assembly toelevated temperature and pressure conditions sufficient to infuse thelayer of fibers with the heat curable composition to form a prepreg.

Another such process for producing a prepreg, includes the steps of (a)providing a layer of fibers; (b) providing the inventive heat curablecomposition in liquid form; (c) passing the layer of fibers through theliquid heat curable composition to infuse the layer of fibers with theheat curable composition; and (d) removing excess heat curablecomposition from the prepreg assembly.

The fiber layer may be constructed from unidirectional fibers, wovenfibers, chopped fibers, non-woven fibers or long, discontinuous fibers.

The fiber chosen may be selected from carbon, glass, aramid, boron,polyalkylene, quartz, polybenzimidazole, polyetheretherketone,polyphenylene sulfide, poly p-phenylene benzobisoaxazole, siliconcarbide, phenolformaldehyde, phthalate and napthenoate.

The carbon is selected from polyacrylonitrile, pitch and acrylic, andthe glass is selected from S glass, S2 glass, E glass, R glass, A glass,AR glass, C glass, D glass, ECR glass, glass filament, staple glass, Tglass and zirconium oxide glass.

The invention further contemplates a towpreg formed from a bundle ofsuch fibers infused with the inventive heat curable composition.

In this regard, the invention relates also to processes for producing atowpreg. In one such process, the steps include (a) providing a bundleof fibers; (b) providing the heat curable composition and (c) joiningthe heat curable composition and the bundle of fibers to form a towpregassembly, and exposing the resulting towpreg assembly to elevatedtemperature and pressure conditions sufficient to impregnate the bundleof fibers with the heat curable composition to form a towpreg.

In another such process, the steps include (a) providing a bundle offibers; (b) providing the inventive heat curable composition in liquidform; (c) passing the bundle of fibers through the liquid heat curablecomposition to impregnate the bundle of fibers with the heat curablecomposition; and (d) removing excess heat curable composition from thetowpreg assembly, thereby forming the towpreg.

The inventive composition may also include an additional toughenercomponent, examples of which include poly(propylene) oxide;amine-terminated polyethylene sulfide, such as PES 5003P, availablecommercially from Sumitomo Chemical Company, Japan; core shell polymers,such as PS 1700, available commercially from Union Carbide Corporation,Danbury, Conn.; and BLENDEX 338, SILTEM STM 1500 and ULTEM 2000, whichare available commercially from General Electric Company. ULTEM 2000(CAS Reg. No. 61128-46-9) is a polyetherimide having a molecular weight(“Mw”) of about 30,000±10,000.

The inventive composition may be in the form of an adhesive, in whichcase one or more of an adhesion promoter, a flame retardant, a filler, athermoplastic additive, a reactive or non-reactive diluent, and athixotrope should be included. In addition, the inventive adhesive maybe placed in film form, in which case a support constructed from nylon,glass, carbon, polyester, polyalkylene, quartz, polybenzimidazole,polyetheretherketone, polyphenylene sulfide, poly p-phenylenebenzobisoaxazole, silicon carbide, phenolformaldehyde, phthalate andnapthenoate should be included.

Compositions of the present invention may ordinarily be cured by heatingto a temperature in the range of about 120 to about 180° C. for a periodof time of about 30 minutes to 4 hours. Thus, the inventive compositionscan be used at relatively moderate temperatures to achieve very goodproductivity.

The inventive compositions (and pregregs and towpregs preparedtherefrom) are particularly useful in the manufacture and assembly ofcomposite parts for aerospace and industrial end uses, bonding ofcomposite and metal parts, core and core-fill for sandwich structuresand composite surfacing.

The invention also provides a process for producing a heat curablecomposition. The steps of this process includes:

(a) providing a benzoxazine comprising

where o is 1-4, X is a direct bond (when o is 2), alkyl (when o is 1),alkylene (when o is 2-4), carbonyl (when o is 2), thiol (when O is 1),thioether (when o is 2) sulfoxide (when o is 2), sulfone (when O is 2)and R₁ is alkyl;

(b) providing with mixing a toughener component comprisingacrylonitrile-butadiene co-polymer having secondary amine terminalgroups; and

(c) mixing the benzoxazine and the toughener component under conditionsappropriate to produce the heat curable composition.

This invention is further illustrated by the following representativeexamples.

EXAMPLES

In a first comparative example, the following components were used toprepare Sample Nos. 1-2 as noted in Table 1.

TABLE 1 Sample No./Amt. (parts) Component 1 2 Benzoxazine* 75 75 Epoxy**25 25 ATBN — 10 *believed to have been made from bisphenol F,thiodiphenol, aniline and formaldehyde, and is available from Vanticounder trade designation RD 2001-081. **CY179, commercially availablefrom Vantico.

Each of the samples was prepared as follows:

The benzoxazine was warmed at a temperature in the range of 180-200° F.to render it flowable, without initiating curing.

Where an epoxy component was present, the flowable benzoxazine was mixedwith the epoxy at a temperature of 180° F. until a homogeneous mixturewas formed.

Where ATBN was present, the ATBN was mixed into the mixture at atemperature in the range of 160-180° F.

The composition so formed was mixed under a vacuum, at a temperature inthe range of 160-180° F. for a period of time of 15-30 minutes. The soformed composition was stored in a closed container at room temperature.

The samples noted in Table 1 may be cured in an open face mold placed inan autoclave using the following cure profile:

The samples were exposed to 90 psi pressure within the autoclave and thetemperature therein was increased at a 5° F./min ramp rate to atemperature of 350° F., for a period of time of about 3 hours. The curedsamples were then cooled to a temperature of about 90° F. in the mold ata 520 F./min ramp rate for a period of time of about 1 hour before useor evaluation.

The cured samples were evaluated using the following property tests:

Dynamic mechanical thermal analysis (“DMTA”) was performed on curedsamples using a double cantilever fixture. The cured samples wereisothermally equilibrated at a temperature of 4020 C. in an oven and thetemperature was increased at a 5° C./min ramp rate to a temperature of250° C. Tg values were obtained from this DMTA evaluation from onset G′,storage shear modulus.

The cured samples were also subjected to boiling water for 3 days, andweight gain was recorded. Tg values were obtained from these samplesusing a DMTA evaluation.

Density of uncured and cured samples was measured according to ASTM D792, and cure shrinkage was then calculated.

Flexure strength and modulus was determined in accordance with ASTM D790, using cured samples with the following specimen dimensions:0.125×0.5×4 in., span 2 in., test speed: 0.05 in./min.

K_(IC) and G_(IC) was determined in accordance with ASTM D5045-96, usingsingle edge notch bending (“SENB”) specimens of the cured samples.

The results of these evaluations on Sample Nos. 1-2 are set forth inTable 2.

TABLE 2 Sample No. Properties 1 2 Cured density 1.24 1.20 Cure shrinkage— −1.8 T_(g), ° C. 192 190 Hot/Wet T_(g), ° C. 158 159 Moisture uptake1.8 2.1 Flexure strength 17 15 Flexure modulus 0.70 0.50 G_(IC),in-lb./in² 0.6 1.4

In comparing these results from Sample Nos. 1 and 2, it is clear that Tgdid not change appreciably by the addition of ATBN in thisbenzoxazine-epoxy system. Also, fracture toughness in terms of G_(IC)increased over two fold. However, the comparison between Tg and Hot/WetTg of Sample Nos. 1-2 each had a large decrease. This is undesirablebecause under service conditions, a finished part made with such acomposition would experience a low service temperature.

Next, Sample Nos. 3-11, which are within the scope of the invention,were prepared using Bm-type benzoxazine and, where noted, ATBN in theamounts noted in Tables 3a and 3b. Sample No. 3, without ATBN, was usedfor comparative purposes.

TABLE 3a Sample No./Amt. (parts) Components 3 4 5 6 7 B-m type 100 95 9085 80 Benzoxazine ATBN — 5 10 15 20

TABLE 3b Sample No./Amt. (parts) Components 8 9 10 11 B-m type 70 60 5040 Benzoxazine ATBN 30 40 50 60

The preparation process for each of Sample Nos. 3-11 was as describedabove with respect to Sample Nos. 1-2, as was the cure profile.

Sample Nos. 3-11 were cured and evaluated for property performance,results of which are shown below in Tables 4a and 4b.

TABLE 4a Sample No. Properties 3 4 5 6 7 ΔH, J/g −213 −207 −173 −168−154 Cured density 1.12 1.09 Cure shrinkage 1.0 T_(g), ° C. 177 180 188197 202 Hot/Wet T_(g), ° C. 168 170 182 190 202 Moisture uptake 1.1 1.11.1 1.5 1.3 G_(IC), in-lb. /in² 0.7 2.3 1.9 2.3 3.2

TABLE 4b Sample No. Properties 8 9 10 11 ΔH, J/g −100 −76 −54 −45 Cureddensity 1.08 1.04 1.00 0.99 Cure shrinkage T_(g), ° C. 204 204 227 232Hot/Wet T_(g), ° C. 208 217 222 232 Moisture uptake 1.1 1.4 1.7 2.2G_(IC), in-lb./in² 4.0

In comparing these results from Sample Nos. 3-11, it is clear that Tgincreased with the addition of ATBN into the Bm-type benzoxazine. Also,fracture toughness in terms of G_(IC) increased with increased amountsof ATBN. And, the comparison between Tg and Hot/Wet Tg of Sample Nos.3-11 showed that there was not an appreciable difference in thesevalues, quite unlike the values observed with Sample Nos. 1-2.

For further comparative purposes, Sample Nos. 12-20 were prepared usingeither a bisphenol F-type, bisphenol A-type, Bm-type benzoxazine (asindicated) and, where noted, an epoxy resin, together with thetougheners indicated, ATBN in the amounts noted in Tables 5a and 5b.

TABLE 5a Components Sample No./Amt. (parts) Type Identity 12 13 14 15 16Benzoxazine B-m — — — — — Bisphenol F 75 75 50 55 58 Bisphenol A — — — —— Epoxy CY 179 25 25 50 45 42 Toughener ATBN — 10 — — — SILTEM* — — 13 —— PES 5003P** — — —  9 17 CTBN — — — — —

TABLE 5b Components Sample No./Amt. (parts) Type Identity 17 18 19 20Benzoxazine B-m — — 100 100 Bisphenol F 100 — — — Bisphenol A — 80 — —Epoxy CY 179 — 20 — — Toughener ATBN — — — 18 SILTEM* — — — — PES5003P** — — — — CTBN 10 — — — *Co-polymer of ULTEM 2000 and siloxane**Polyether sulfone, commercially available from Sumitomo

The preparation process for each of Sample Nos. 12-20 was as describedabove with respect to Sample Nos. 1 and 2, as was the cure profile.

Performance property evaluation of Sample Nos. 12-20 was performed asfollows, with the results recorded in Tables 6a-6b.

Uncured samples were evaluated by Differential Scanning Calorimetry(“DSC”), within a temperature range of 40-350° C., where the temperaturerange increased at a 20° C./min ramp rate, and from which ΔH wasrecorded.

Cured samples were evaluated as above.

TABLE 6a Sample No. Property 12 13 14 15 16 ΔH, J/g −367 −320 −340 −266−263

TABLE 6b Sample No. Property 17 18 19 20 ΔH, J/g −353 −431 −213 −168

Reference to FIGS. 1-3 shows that with the inventive composition(illustrated in FIG. 1), an increase of ATBN concentration improvesG_(IC) and dry Tg and Hot/Wet Tg, while with benzoxazines outside of theclaimed structure (illustrated in FIGS. 2-3), an increase of ATBNconcentration improves G_(IC) but decreases Tg. FIG. 1 shows that in theinventive composition Tg and toughness measured by G_(Ic) increase asthe amount of toughener in the composition increases, whereas FIGS. 2and 3 show that with either an aryl substituted benzoxazine (that is,where R₁ and/or R₂) and/or CTBN instead of ATBN the opposite result isillustrated.

An increased Tg such as 200 (dry), together with increased toughnesssuch as 3, are not ordinarily found in the same thermoset system. Oneknown exception to this is Cytec Industries 977-2, which provides anepoxy prepeg thermoset. However, this Cytec product is known to have amoisture uptake of about 3 to 5%, which contributes to low Hot/Wet Tg(such as about 300), and a high ΔH, such as 500-700 J/g, compared to theinventive compositions, which are demonstrated to be lower than 500 J/gwith one as low as 163 J/g. A lower ΔH is desirable so that stresseswithin the assembled structure are not caused during cooling. And thethermosets from the inventive compositions have the potential to reachan increased Tg ordinarily not found, unless insoluble toughenermaterials are added, or have an unacceptable viscosity for manycommercial applications.

1. A prepreg comprising a layer of fibers infused with a heat curablecomposition comprising: (a) a benzoxazine component comprising

wherein o is 1-4, X is member selected from the group consisting of adirect bond (when o is 2), alky (when o is 1), alkylene (when o is 2-4),carbonyl (when o is 2), thiol (when o is 1), thioether (when o is 2),sulfoxide (when o is 2), and sulfone (when o is 2) , and R₁ is alkyl;and (b) about 5 weight percent or more of a toughener componentcomprising acrylonitrile-butadiene co-polymer having secondary amineterminal groups.
 2. The prepreg of claim 1, wherein the fiber layer ismade from unidirectional fibers.
 3. The prepreg of claim 1, wherein thefiber layer is made from woven fibers.
 4. The prepreg of claim 1,wherein the fiber is selected from the group consisting of carbon,glass, aramid, boron, polyalkylene, quartz, polybenzimidazole,polyetheretherketone, polyphenylene sulfide, poly p-phenylenebenzobisoaxazole, silicon carbide, phenolformaldehyde, phthalate andnapthenoate.
 5. The prepreg of claim 4, wherein the glass is a memberselected from the group consisting of S glass, S2 glass, E glass, Rglass, A glass, AR glass, C glass, D glass, ECR glass, glass filament,staple glass, T glass and zirconium oxide glass.
 6. The prepreg of claim4, wherein the carbon is a member selected from the group consisting ofpolyacrylonitrile, pitch and acrylic.
 7. Cured reaction products of theprepreg of claim
 1. 8. A prepreg made by a process for producing aprepreg, steps of which comprise: (a) providing a layer of fibers; (b)providing a heat curable composition comprising: (i) a benzoxazinecomponent comprising

wherein o is 1-4, X s member selected from the group consisting of adirect bond (when o is 2), alkyl (when o is 1), alkylene (when o is2-4), carbonyl (when o is 2), thiol (when o is 1), thioether (when o is2), sulfoxide (when o is 2), and sulfone (when o is 2), and R₁ is alkyl;and (ii) about 5 weight percent or more of a toughener componentcomprising acrylonitrile-butadiene, co-polymer having secondary amineterminal groups; and (c) joining the heat curable composition and thelayer of fibers to form a prepreg assembly, and exposing the resultingprepreg assembly to elevated temperature and pressure conditionssufficient to infuse the layer of fibers with the heat curablecomposition to form a prepreg.
 9. A prepreg made by a process forproducing a prepreg, steps of which comprise: (a) providing a layer offibers; (b) providing a heat curable composition comprising: (i) abenzoxazine component comprising

wherein o is 1-4, X is member selected from the group consisting of adirect bond (when o is 2), alkyl (when o is 1) alkylene (when o is 2-4),carbonyl (when o is 2), thiol (when o is 1), thioether (when o is 2),sulfoxide (when o is 2), and sulfone (when o is 2), and R₁ is alkyl; and(ii) about 5 Weight percent or more of a toughener component comprisingacrylonitrile-butadiene co-polymer having secondary amine terminalgroups in liquid form; (c) passing the layer of fibers through theliquid heat curable composition to infuse the layer of fibers with theheat curable composition; and (d) removing excess heat curablecomposition from the prepeg assembly.
 10. Cured reaction product of theprepreg of claim
 8. 11. Cured reaction product of the prepreg of claim9.
 12. A towpreg comprising: (a) a bundle of fibers infused with a heatcurable composition comprising: (i) a benzoxazine component comprising

wherein o is 1-4, X is member selected from the group consisting of adirect bond (when o is 2), alkyl (when o is 1), alkylene (when o is2-4), carbonyl (when o is 2), thiol (when o is 1), thioether (when o is2), sulfoxide (when o is 2), and sulfone (when o is 2), and R₁ is alkyl;and (ii) about 5 weight percent or more of a toughener componentcomprising acrylonitrile-butadiene co-polymer having secondary amineterminal groups.
 13. The towpreg of claim 12, wherein the fibers areselected from the group consisting of carbon, glass, aramid, boron,polyalkylene, quartz, polybenzimidazole, polyetheretherketone,polyphenylene sulfide, poly p-phenylene benzobisoaxazole, siliconcarbide, phenolformaldehyde, phthalate and napthenoate.
 14. The towpregof claim 13, wherein the glass is a member selected from the groupconsisting of S2 glass, E glass, R glass, R glass, A glass, AR glass, Cglass, D glass, ECR glass, glass filament, staple glass, T glass andzirconium oxide glass.
 15. The towpreg of claim 13, wherein the carbonis a member selected from the group consisting of polyacrylonitrile,pitch and acrylic.
 16. Cured reaction products of the towpreg of claim12.
 17. A towpreg made by a process for producing a towpreg, steps ofwhich comprise: (a) providing a bundle of fibers; (b) providing a heatcurable composition comprising: (i) a benzoxazine component comprising

wherein o is 1-4, X is member selected from the group consisting of adirect bond (when o is 2), alkyl (when o is 1), alkylene (when o is2-4), carbonyl (when o is 2), thiol (when o is 1), thioether (when o is2), sulfoxide (when o is 2), and sulfone (when o is 2), and R₁ is alkyl;and (ii) about 5 weight percent or more of a toughener componentcomprising acrylonitrile-butadiene co-polymer having secondary amineterminal groups; and (c) joining the heat curable composition and thebundle of fibers to form a towpreg assembly, and exposing the resultingtowpreg assembly to elevated temperature and pressure conditionssufficient to impregnate the bundle of fibers with the heat curablecomposition to form a towpreg.
 18. A towpreg made by a process forproducing a towpreg, steps of which comprise: (a) providing a bundle offibers; (b) providing a heat curable composition comprising: (i) abenzoxazine component comprising

wherein o is 1-4, X is member selected from the group consisting of adirect bond (when o is 2), alkyl (when o is 1), alkylene (when o is2-4), carbonyl (when o is 2), thiol (when o is 1), thioether (when o is2), sulfoxide (when o is 2), and sulfone (when o is 2), and R₁ is alkyl;and (ii) about 5 weight percent or more of a toughener componentcomprising acrylonitrile-butadiene co-polymer having secondary amineterminal groups in liquid form; (c) passing the bundle of fibers throughthe liquid heat curable composition to impregnate the bundle of fiberswith the heat curable composition; and (d) removing excess heat curablecomposition from the towpreg assembly, thereby forming a towpreg. 19.Cured reaction product of the towpreg of claim
 17. 20. Cured reactionproduct of the towpreg of claim
 18. 21. An adhesive film comprising aheat curable composition comprising: (a) a benzoxazine componentcomprising

wherein o is 1-4, X is member selected from the group consisting of adirect bond (when o is 2), alkyl (when o is 1), alkylene (when o is 2-4)carbonyl (when o is 2) thiol (when o s 1), thioether (when o is 2),sulfoxide (when o is 2), and sulfone (when o is 2), and R₁ is alkyl; and(b) about 5 weight percent or more of a toughener component comprisingacrylonitrile-butadiene co-polymer having secondary amine terminalgroups.
 22. The adhesive film of claim 21, further comprising a supportselected from the group consisting of nylon, glass, carbon, polyester,polyalkylene, quartz, polybenzimidazole, polyetheretherketone,polyphenylene sulfide, poly p-phenylene benzobisoaxazole, siliconcarbide, phenolformaldehyde, phthalate and napthenoate.
 23. Curedreaction product of the adhesive film of claim 21.